The present invention relates to a security device.
A large number of security devices are provided in relation to high-security documents, in particular identity documents like passports, identity cards, driving licenses and the like as well as payment means like credit cards, bank notes and the like. This involves, for example, the provision of security devices which are visible to the human eye like holograms. In addition, there are also provided security devices which are not visible to the human eye or which are visible only under special light and which are produced, for example, by dye pigments introduced into the high-security document.
WO 94/28444 A1 and WO 95/02200 A1 describe the production and function of diffractive security features produced by the combination of various conventional diffractive security features like pixelgrams, kinegrams, mathematical holograms and the like. In the case of WO 95/02200 A1 the combination is generated by the superpositioning of the associated grating structures in at least one part of the surface of the combined security feature. WO 94/28444 A1 in contrast relates to a pixelated security feature whose individual pixels are subdivided into subpixels, wherein each individual one of those subpixels is configured in accordance with precisely one of the original security features. The totality of the subpixels is thus subdivided into groups of subpixels, wherein each group represents precisely one of the original security features. In that case the arrangement of the subpixels of a group follows a regular pattern as the association of the subpixels with the respective group remains the same within the higher-level pixels of the combined security feature.
Both WO 94/28444 A1 and also WO 95/02200 A1 thus describe possible ways of superpositioning various diffractive security features in such a way that the viewer can perceive those features on the same surface, wherein the visibility of the individual features is influenced by the combination of illumination and observation angles.
WO 2010/115936 discloses a security device which is particularly suitable for payment means. It has a reflection layer like an aluminum film on the top side of which is arranged a multiplicity of diffractive surface elements. The individual surface elements have a sinusoidal surface structure for producing a diffraction grating. The individual surface elements in that case are of such a configuration that incident light is diffracted in such a way as to give the observer an impression similar to natural asterism. An observer thus sees, for example, a star-shaped symbol which rotates about itself in an image plane.
A security device with another movement effect is described in WO 02/03109. This involves a holographic optically variable image which is produced by a grating structure which is continuously variable as a function of location. The representation of that image follows a predetermined path when the security device is tilted in a first direction. To achieve a sharp image when viewing under white light in that case only a narrow wavelength range is shown in the manner of a rainbow hologram, the wavelength range depending on the rotation of the security device perpendicularly to the first direction. In the case of a tilting movement in that second direction therefore no movement is observed, but instead a change in color.